1. Field of the Invention
The present invention relates to a navigation apparatus for a mobile body, and more particularly to display processing for a navigation apparatus which is mounted in a vehicle. The present invention also relates to a map display apparatus, and more particularly to a map display apparatus suitable for use in a navigation system for a mobile body.
2. Description of Background Information
Conventional stand-alone navigation apparatuses, such as a position detecting apparatus for a variety of mobile bodies such as automotive vehicles, aircraft, ships, and so on, have been known in the art. The stand-alone navigation system is structured to derive a two-dimensional displacement (a vector amount) of a mobile body from azimuthal data from an azimuth sensor and velocity data from a velocity sensor, and detect a current position of the mobile body by accumulating this two-dimensional displacement to a reference point. For example, when applied to a vehicle, an accumulated traveled distance derived from a traveled distance sensor and an accumulated azimuth derived from an azimuthal sensor are accumulated on a reference point, to determine a current position (data). More specifically, for example, a correspondence between a rotational speed of a driving shaft and a number of pulses generated by a rotational speed sensor mounted on the driving shaft is previously established. An accumulated traveled distance is derived by multiplying a distance calculated from a total number of pulses generated from the reference point to the current position with a distance correcting coefficient, and an accumulated azimuth is then derived by accumulating the azimuth detected by a geomagnetic sensor.
In addition, a GPS (Global Positioning System) navigation apparatus has been developed as a position detecting apparatus utilizing artificial satellites. This GPS navigation apparatus receives radio wave signals generally from three or more GPS satellites, and virtual distance data including a time offset of the receiver between each GPS satellite and a received point (vehicle's position) and positional data of each GPS satellite are used to detect a current position (data) of the received point.
These position detecting apparatus have been implemented as actual navigation apparatus ranging from a simple system which indicates the latitude and longitude of a current position with numerical values to a high-level system which displays a variety of data including an vehicle's position, a distance to a destination, a moving speed and so on on a map displayed on the screen of a CRT (Cathode Ray Tube) unit.
A navigation system which displays a variety of data on a CRT screen reads map data including a derived current position from a storage medium such as CD-ROM, creates screen data from the read map data and detected current position data, and outputs the created data to the CRT unit for displaying a map thereon. This display screen allows a user to know his or her current position in relation to the map. Further, the abovementioned conventional navigation apparatuses include such an apparatus which displays the latitude and longitude of the position of a mobile body on a CRT screen with numerical values.
The above-mentioned conventional navigation apparatus, however, has a disadvantage in that it is not capable of calculating coordinate data (latitude and longitude) of an arbitrary position on a map displayed on the CRT unit. For example, when a common destination is to be set in a plurality of navigation apparatuses existing at remote positions from one another, it is difficult to correctly communicate the destination to correspondents particularly in an unknown region. A like problem may also arise among navigation apparatuses, where each is arranged to display the coordinates of their vehicle's positions with numerical values, where even though each apparatus can communicate with another about the coordinates of a current vehicle's position, it is difficult to immediately understand the relative positional relationship between these apparatuses.
FIG. 1 shows an example of a conventional display for navigation on the screen. The display on the screen includes a map MP in which indicated are the positions of buildings or the like which may serve as guides (represented by " " in the drawing), their names (indicated by ABC, DEF in the drawing) and so on. On the upper left side of the map MP, there is displayed a distance scale DS for this map. In a central portion of the screen, there are displayed the current vehicle's position (indicated by a triangular mark) P and a range scale DSC from the current vehicle's position. If the coordinates of a destination (for example, the latitude and longitude) have previously been input, the azimuth X from the current position (indicated by an arrow in the drawing) and the straight distance LD from the current position are also displayed on the map MT as destination information.
In the conventional navigation system as described above, since the destination information displayed on the CRT screen only provides the azimuth and straight distance from the current position (vehicle's position) to the destination, when a user has set several locations on the way to the final destination (such a location will hereinafter be referred to as a "route point") as intermediate destinations, the user may sometimes forget which are such intermediate destinations, thereby causing to the user anxiety about the destination to which he or she is running.
Incidentally, the user sometimes desires to refer to a map around a particular destination. For example, when the user is going to a .DELTA..DELTA. building near OO station, he or she will refer to a map around the OO station. The conventional navigation system has a mode which displays a name list of locations to be displayed to allow the user to select a location from the list, and display a map around the selected location (this mode will hereinafter be referred to as "the atlas mode").
The operation of the navigation system in the atlas mode will be explained below with reference to FIGS. 2-8. It is assumed herein that stored data on a name list is classified according to the category of locations to be displayed. More specifically, location data may be classified into the following four categories: 1. location name list data which has been stored as initial data in the navigation system and includes names of stations, crossovers and so on and the latitude and longitude thereof; 2. user registered location data which is personal location data previously stored in the navigation system such as the user's private residence, office and so on; 3. destination data which is location data on the final destination set by the user; and 4. route point data which is location data on intermediate destinations which are manually set by the user or automatically retrieved by the navigation system and are to be passed through for reaching the final destination.
Prior to the explanation of the operation, a data storing format of the name list will be explained below.
The location name list data, the user registered location data, the destination data and the route point data are previously stored in a memory, not shown, as packet data. Respective packed data groups DP.sub.1, DP.sub.2, DP.sub.3, DP.sub.4 of the location name list data, the user registered location data, the destination data and the route point data are sequentially stored from previously determined storage start addresses thereof L.sub.0, T.sub.0, M.sub.0, K.sub.0, as shown in FIG. 2. Numbers of packets constituting the respective packet data groups DP.sub.1, DP.sub.2, DP.sub.3, DP.sub.4 are stored in a predetermined storage area of the memory, not shown, as the number of location name list packets NL; the number of user registered location packets NT; the number of destination packet numbers NM (=1); and the number of route point packets NK, as shown in FIG. 3(a). Also, each packet data constituting each of the packet data groups comprises latitude numerical value data D.sub.LA indicative of the latitude of a particular location; longitude numerical value data D.sub.LO indicative of the longitude of the particular location; and Chinese character code data DCH of a name character string, as shown in FIG. 3(b).
Now, the operation of the atlas mode will be explained below. A screen on the display unit in the atlas mode is divided into a mode display area MAR for displaying an operation mode corresponding to a display on the screen and instructions to prompt the user to input; first to fifth item display areas IAR.sub.0 -IAR.sub.4 for displaying items to be selected; and a manipulation instruction area HAR for displaying a variety of manipulation instructions, as shown in FIG. 4. The first to fifth item display areas IAR.sub.0 -IAR.sub.4 correspond to selected frame numbers Col=0-4, respectively.
First, when the user selects the atlas mode, an atlas mode initial screen FL.sub.1 as shown in FIG. 5 is displayed on the display unit. Then, the navigation system asks the user from which of the location name list data, the user registered location data, the final destination data and the route point data a location to be displayed is selected. The user then manipulates cursor keys to point a cursor on a desired data category and depresses a determination key, not shown, to select the data category. More specifically, in FIG. 5, since the frame of the currently selected data category (the frame of the user registered location data) is reversely displayed (represented by hatching in the drawing), depression of the determination key, not shown, in this state results in displaying a screen FL.sub.3 for selecting user registered location data as shown in FIG. 6.
Next, the above described operation will be explained in greater detail with reference to operation flowcharts of FIGS. 7 and 8.
When the user selects the atlas mode, the atlas mode initial screen (see FIG. 5) is displayed. If the user has selected the location name list data on the atlas mode initial screen, which is determined by step S51, the flow proceeds to step S55, where a data storage start address Top is set to L.sub.0, and a data storage end address Tail is set to NL-1, followed by the flow proceeding to step S60. On the other hand, if the location name list data has not been selected at step S51, the flow proceeds to step S52.
If it is determined at step S52 that the user registered location data has been selected on the atlas mode initial screen, the flow proceeds to step S56, where the data storage start address Top is set to T.sub.0, and the data storage end address Tail is set to NT-1. Then, the flow proceeds to step S60. Contrarily, if the user registered location data has not been selected at step S52, the flow proceeds to step S53.
If it is determined at step S53 that the destination data has been selected on the atlas mode initial screen, the flow proceeds to step S57. where the data storage start address Top is set to M.sub.0, and the data storage end address Tail is set to NM-1. The flow then proceeds to step S60. Contrarily, if the destination data has not been selected at step S53, the flow proceeds to step S54.
If it is determined at step S54 that the route point data has been selected on the atlas mode initial screen, the flow proceeds to step S58, where the data storage start address Top is set to K.sub.0, and the data storage end address Tail is set to NK-1. The operation then proceeds to step S60.
Referring next to FIG. 8, a start packet number Ptr is set to the data storage start address Top, and a selected frame number Col is set to zero (step 60).
Then, if it is determined, at step S62, that an upward moving key (.uparw.) has been depressed, the flow proceeds to step S71, where it is determined whether or not the selected frame number Col is equal to zero (Col=0). If the selected frame number Col is not equal to zero (Col.noteq.0), Col is decremented by one at step S72 (Col=Col-1), and thereafter the flow returns to step S61. If the selected frame number Col is equal to zero (Col=0), it is determined at step S73 whether or not the start packet number Ptr is larger than the data storage start address Top. If Ptr&gt;Top, Ptr is decremented by one at step S74 (Ptr=Ptr-1), and the flow returns to step S61. Conversely, if Ptr.ltoreq.Top, the flow immediately returns to step S61.
At step S62, if the upward moving key is not depressed, the flow proceeds to step S63 to determine whether or not a downward moving key (.dwnarw.) has been depressed. If so, the flow proceeds to step S67. At step S67, it is determined whether or not the selected frame number Col is equal to four (Col=4). If the selected frame number Col is not four (Col.noteq.4), Col is incremented by one (Col=Col+1) at step S68, and then the flow again returns to step S61.
If the selected frame number Col is equal to four (Col=4), it is determined at step S69 whether or not the start packet number Ptr plus four is larger than the data storage end address Tail (Ptr+4&gt;Tail). If Ptr+4&lt;Tail, Ptr is incremented by one (Ptr=Ptr+1) at step S70, and then the flow returns to step S61. Conversely, if Ptr+4&gt;Tail, the flow immediately jumps to step S61.
If neither the upward moving key (.uparw.) nor the downward moving key (.dwnarw.) has been depressed but any other key has been depressed instead, the flow immediately returns to step S61 by the determination of step S64.
If the determination at step S64 indicates that a selection key has been depressed, latitude data and longitude data are fetched at step S65 from packet data, the packet number of which is expressed by the start packet number Ptr plus the selected frame number Col (Ptr+Col), and a map around the location corresponding to the fetched latitude data and longitude data is displayed at step S66.
In the above described conventional navigation system, however, in order to display a screen FL.sub.4 for selecting route point data after terminating the screen FL.sub.3 for selecting user registered location data, for example, the route point data selection screen FL.sub.4 need be selected after the display is once returned to the atlas mode initial screen FL.sub.1.
Thus, the conventional navigation system has a disadvantage that a larger number of procedures and manipulation steps are required to obtain desired map information, which leads to complicated manipulations.